The goal of this project is to develop a novel human monoclonal antibody-targeted small interfering RNA (siRNA) therapeutic that has the potential to be first-in-its-kind for treating tumor and metastasis. We have previously identified a panel of rapidly internalizing human single chain antibodies (scFvs) that target clinically represented tumor cell surface antigens. These scFvs were selected from phage antibody display libraries using laser capture microdissection for their ability to bind to tumor cells in situ residing in thir tissue microenvironment, and to mediate efficient intracellular payload delivery to tumor cells. We have in addition identified novel siRNA binding motifs that can be joined with our internalizing scFv and produced as a fusion protein that gains the tumor-targeted intracellular siRNA delivery functions. We propose to develop a novel class of scFv-targeted siRNA therapeutics based on our rapidly internalizing human scFv linked via the novel siRNA binding motif to siRNAs that target genes critical for tumor cell survival. PUBLIC HEALTH RELEVANCE: Small interfering RNA (siRNA) has the potential to be a novel class of therapeutics due to its potent and specific effects on target genes. While siRNA has become an effective research tool, its therapeutic application has been hindered by the lack of an effective technology for targeted systemic delivery in vivo. The goal of this project is to develop novel human antibody-targeted systemic siRNA delivery vehicle that could eventually lead to a new class of therapeutics for treating tumor and cancer metastases. We have previously identified a panel of rapidly internalizing human single chain antibodies (scFvs) that target clinically represented prostate cancer cell surface antigens. These scFvs were selected from phage antibody display libraries using laser capture microdissection for their ability to bind to tumor cells in situ residing in their tissue microenvironment, and to mediate efficient intracellular payload delivery to castration resistant prostate cancer cells. We have in addition identified novel siRNA binding motifs that can be joined with our internalizing scFv and produced as a fusion protein that retains tumor targeting and siRNA binding functions. We propose to develop tumor- targeted systemic siRNA delivery vehicles based on our rapidly internalizing human scFv to modulate genes critical for tumor growth and survival.